In an internal combustion engine, for example, it is known that a technique in which the oxygen concentration in exhaust gas, the air-fuel ratio state, and the like are detected and a combustion control is conducted on the basis of detected values is very effective for energy saving, purification of exhaust gas, etc. As a sensor for detecting the oxygen concentration or the like in exhaust gas (to-be-measured gas), known is a gas sensor in which a detecting element made of a solid electrolyte such as zirconia is used. Various improvements have been applied on such a gas sensor.
For example, JP-A-2001-147213 discloses a gas sensor 1001 shown in FIG. 1. The gas sensor 1001 is an oxygen sensor which is to be used in an internal combustion engine for an automobile, and has: a detecting element 1010 having a gas-exposed portion 1011 which is to be in contact with to-be-measured gas; a metal shell 1004 which holds the detecting element 1010 in the state where the gas-exposed portion 1011 is exposed; and a protective cover 1002 which is disposed from the metal shell 1004 to cover the gas-exposed portion 1011 of the detecting element 1010. The gas sensor further has: two lead terminals 1071, 1072 which are electrically connected to the detecting element 1010; plural lead wires 1081, 1091 which are to be electrically connected to them, respectively; connectors 1075, 1076 through which the lead terminals 1071, 1072 are connected to the lead wires 1081, 1091; an electrically insulative insulating member 1005 which provides insulation between the connectors 1075, 1076, and a first metal cover 1003 in which the insulating member 1005 is housed. A heater 1015 which is placed inside the detecting element 1010 in order to heat the detecting element 1010 is connected to the outside through a lead wire 1171 and another lead wire which is not shown.
The insulating member 1005 has: a main portion 1051 which houses a part of the lead wires 1081, 1091, 1171, the connectors 1075, 1076, and the like; and a flange portion 1052 which is larger in diameter than the main portion 1051. The first metal cover 1003 has: a small-diameter portion 1031 having an inner diameter which is larger than the outer diameter of the main portion 1051 of the insulating member 1005, and which is smaller than the outer diameter of the flange portion 1052; a large-diameter portion 1032 having an inner diameter which is larger than the outer diameter of the flange portion 1052; and a step portion 1033 which connects the small-diameter portion 1031 with the large-diameter portion 1032.
In the insulating member 1005, one face (the upper face in the figure) 1521 of the flange portion 1052 butts against the step portion 1033, and the other face (the lower face in the figure) 1522 of the flange portion 1052 is pressed and fixed by an elastic member 1006 which is pressingly inserted into the large-diameter portion 1032. Namely, the insulating member 1005 is fixed with being clamped between the elastic member 1006 and the step portion 1033 of the first metal cover 1003.
According to the configuration, unlike a conventional gas sensor, the gas sensor 1001 is not required to have a structure in which an insulating member is fixed by combining plural covers. Since the insulating member 1005 is fixed by using the elastic member 1006, the joining position between the first metal cover 1003 and the metal shell 1004, and the like are not affected even when the size of the insulating member 1005 is dispersed. Consequently, there are advantages such as that the dimension accuracy of the total length of the gas sensor 1001 can be improved.
In the gas sensor 1001, as described above, the insulating member 1005 is fixed by causing the face 1521 of the flange portion 1052 of the insulating member 1005 which face is substantially perpendicular to the axial direction (the vertical direction in FIG. 1) to butt against the step portion 1033 of the first metal cover 1003 which step portion is similarly perpendicular to the axial direction. However, the outer diameter of the flange portion 1052 of the insulating member 1005 is smaller than the inner diameter of the large-diameter portion 1032 of the first metal cover 1003. Consequently, there is the possibility that the insulating member 1005 is fixed to the first metal cover 1003 in an inadequately misaligned state where the axis of the first metal cover 1003 fails to coincide with that of the insulating member 1005. As a result, also a part of the lead wires 1081, 1091, 1171 held in the insulating member 1005, the connectors 1075, 1076, and the like are held with being deviated from their original held positions, so that unwanted stresses are applied to the lead wires 1081, 1091, 1171, the connectors 1075, 1076, and the like. Consequently, there is the possibility that defects including destruction such as bending of the detecting element 1010 or the heater 1015, and breakage or disconnection of the lead wire 1081, the connector 1075, and the like occur.
The gas sensor 1001 is produced in the following manner. First, the insulating member 1005 in a state where the lead wire 1081, the connector 1075, and the like are not housed in the member is previously fixed to the inside of the first metal cover 1003 by using the elastic member 1006. Thereafter, the lead wire 1081, the connector 1075, and the like are housed in the insulating member 1005. The heater 1015 is then inserted into the detecting element 1010, and the first metal cover 1003 is fixed to the metal shell 1004.
However, the work of housing the lead wire 1081, the connector 1075, and the like in the insulating member 1005 in the state where the insulating member 1005 is fixed to the inside of the first metal cover 1003 is cumbersome. It is difficult to house the lead wire 1081, the connector 1075, and the like at adequate positions in the insulating member 1005. When these components fail to be housed at adequate positions, moreover, unwanted stresses are applied to the lead wires 1081, 1091, 1171, the connectors 1075, 1076, and the like in the same manner as the above-mentioned case where positional deviation occurs, and a defect such as breakage or disconnection may occur.
It may be contemplated that, conversely, the lead wire 1081, the connector 1075, and the like are previously housed at adequate positions in the insulating member 1005, and the insulating member 1005 is then fixed to the inside of the first metal cover 1003. However, the lead wire 1081, the connector 1075, and the like are already housed in the insulating member 1005. As compared with the case where these components do not exist, therefore, it is difficult to pressingly insert the elastic member 1006 into the first metal cover 1003, and the work of fixing the insulating member 1005 to the inside of the first metal cover 1003 is cumbersome.
The gas sensor 1001 is produced in the following manner. As described above, first, the insulating member 1005 in which the lead wire 1081 and the like are not housed is fixed to the inside of the first metal cover 1003 by using the elastic member 1006. Thereafter, the lead wire 1081, the connector 1075, and the like are housed in the insulating member 1005. The heater 1015 is then inserted into the detecting element 1010, and the first metal cover 1003 is fixed to the metal shell 1004. Depending on the housed state of the lead wire 1171 and the like housed in the insulating member 1005, there is possibly a case in which the state where the heater 1015 to be connected to them is inclined with respect to the axis of the insulating member 1005 is most stable.
In the production method, however, the heater 1015 is inserted into the detecting element 1010 in the state where the insulating member 1005 is fixed to the inside of the first metal cover 1003. Therefore, the inclination of the heater 1015 is compulsively changed by the insertion. As a result, unwanted stresses are applied to the heater 1015, the lead terminals thereof, the lead wire 1171, and the like, thereby causing the possibility that a defect such as breakage, disconnection, or bending of the heater occurs.
The invention has been conducted in view of the problems. It is an object of the invention to provide a sensor that has a metal outer tube in which terminal members such as a connector are housed and a separator for providing insulation between the terminal members, and the like from one another is housed and fixed, in a manner similar to the insulating member and the first metal cover described above, and that is highly reliable, and also a method of producing a sensor that is highly reliable, and that can be easily produced. It is another object of the invention to provide a method of producing a sensor in which bending of a heater and the like hardly occur. It is a further object of the invention to provide an assembly of a separator and a pressing member that is suitable for production of a sensor.